In future photonic or optical networks including technologies such as optical packet switching, all-optical bistable devices (commonly known as “latches” or “flip flops”) will be key elements to provide for packet buffering, self-routing and bit-length conversion. Few devices and architectures for all-optical bistable devices have been demonstrated, mainly based on the bistable operation of laser diodes and semiconductor optical amplifiers. In particular, some kinds of bistable laser diodes, such as vertical-cavity surface-emitting lasers (see H. Kawaguchi et al., “Pitchfork bifurcation polarization bistability in vertical-cavity surface-emitting lasers”, Electron. Lett., vol. 31, no. 2, pp. 109-111, 1995) and coupled laser diodes (Y. Liu et al., “Three-state all-optical memory based on coupled ring lasers” IEEE Photon. Technol. Lett., vol. 15, no. 10, pp. 1461-1463, October 2003) have been investigated for the realisation of all-optical bistable devices. Furthermore, with the development of optical networks, it is desirable to develop all-optical memories.
By “light”, “optical” and cognate terms herein, we not only refer to visible light, but also Infra Red (IR) and Ultra Violet (UV) light as is common in the art.